After investigating the March 19 death of 15-year-old Yussef Sami Shawamreh, B'Tselem said it had found no evidence to support the army's version of events that troops had opened fire at youths who had "sabotaged" the West Bank security barrier.

B'Tselem said the primary responsibility for the boy's death rested with the army commanders who approved the use of live fire at a site where villagers from Deir al-Asal al-Tahta are known to go out and pick wild plants on their own land.

An army spokeswoman told AFP after the incident that soldiers had spotted three Palestinians vandalizing the barrier, saying they had "verbally warned" them before firing warning shots in the air then shooting at their lower extremities.

But Shawamreh's family and witnesses said the teenager had been looking for gundelia, a thistle-type plant used in cooking.

B'Tselem said the shooting occurred in an area where there is a wide breach in the barrier and where families regularly go out to forage on their own farmland.

"The two surviving youths... heard three or four shots as they got off the road, fired with no advance warning," the report said.

Shawamreh, who was severely wounded but not picked up by a military ambulance for some 30 minutes, was later pronounced dead at an Israeli hospital.

The NGO said its findings were "markedly different" from the army's version of events.

"The youths made no attempt at vandalism; they were crossing through a long-existing breach, and the soldiers did not carry out suspect arrest procedure, shooing at Shawamreh with no advance warning," it said.

Troops in the area were "well aware" that over the past two years, Palestinians have been crossing the barrier at the breach "to pick gundelia on their own farmland," B'Tselem.

It added that the use of live fire showed a "cynical lack of concern for the life of a Palestinian teenager."

Two days earlier, soldiers had detained four teenagers in the same spot, beating them and confiscating the plants they had picked, the NGO said.

"The decision to mount an armed ambush at a point in the barrier known to be crossed by youths, who pose no danger whatsoever to anyone, for the purpose of harvesting plants is highly questionable," the report said, noting it showed "extremely faulty discretion" on the part of the commanders.

Military regulations prohibit the use of live fire at Palestinians crossing the barrier, if they pose no risk to security forces.

"The primary responsibility for the killing lies with the commanders who sent the soldiers out on armed ambush," B'Tselem director Jessica Montell said in a statement that urged the military police to consider whether the commanders should "bear personal criminal responsibility" for Shawamreh's death.